It seems that when God was making the world, he called man over and
  bestowed upon him twenty years of normal sex life. Man was horrified.

  "Only
  twenty years of normal sex life?" but the Lord was very adamant that was
  all
  man could have.

Then the Lord called the monkey and gave him twenty years. "But I don't
  need twenty years", he protested, "Ten is plenty for me."
 

 Then the Lord called the lion and gave him twenty years, and the lion,
  like
  the monkey, wanted only ten.
Again the man spoke up, "Can I have the other ten?" The lion said of
  course
  he could.

Then came the donkey and he was given twenty years - but like the
 others,
  ten was sufficient - and again man pleaded, "Can I have the other ten?"
 

This explains why man has twenty years of normal sex life, plus ten
  years
  of monkeying around, ten years of lion about it, and ten years of making
 an
 ass of himself.